textproduct: Quad Cities

KEY MESSAGES

- Heat and humidity will build across the area for at least the first half of next week. Heat index values are expected to rise to the middle 90s to around 100 degrees, highest for areas south of I- 80. This is dependent on if showers/storms develop, which would cool temperatures.

- There is potential for active weather at times, depending on the where the edge of the heat dome settles.

SHORT TERM /THROUGH SUNDAY/

Issued at 147 PM CDT Sat Aug 29 2026

The area of showers and isolated thunderstorms from this morning will continue to slowly dissipate this afternoon as it makes it way eastward, giving way for dry conditions late this afternoon and evening across the area. With the precipitation and cloud cover, temperatures this afternoon have been slightly cooler across our northeast, with highs in the middle 70s over northwest Illinois and adjacent areas of northeast Iowa, to the middle/upper 80s towards northeast Missouri, southeast Iowa, and west-central Illinois.

Dry conditions are expected this evening before an area of showers and isolated thunderstorms redevelop late tonight into Sunday morning ahead of a 35 to 45 knot south-southwesterly low-level jet. Composite reflectivity paintball fields from the 29.12z HREF and REFS ensembles suggests isolated to scattered showers, with isolated storms, late tonight into Sunday morning, mainly for our eastern and southern portions of the area (20-40% chances). With meager MUCAPE values (<500 J/kg per the HREF), thunderstorm potential appears to be quite low.

The rest of the day Sunday will be noticeably warmer and more humid as mid-level ridging and a heat dome builds over the central CONUS. LREF ensemble cluster analysis is in very good agreement on this occurring, with 500 mb heights of 594 decameters over the southern Plains/southern MS River Valley regions. High temperatures on Sunday are expected to warm to the upper 80s to lower 90s over most of the area, warmest over our southern areas. However, as a weak mid-level shortwave is progged to sweep through the area, this could generate additional showers and storm chances along and north of Highway 30, which could keep temperatures relatively cooler there. So, some uncertainty exists on exactly how warm we will get Sunday for these areas.

LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/

Issued at 147 PM CDT Sat Aug 29 2026

The main focus for the long-term forecast period continues to be on building heat and humidity, especially for Monday through at least Wednesday before relatively cooler conditions return by the end of the week. For areas that avoid any precipitation during this period, confidence is higher for very warm and muggy conditions. The latest ECMWF EFI/Shift of Tails values for high temperatures Monday through Wednesday are in excess of 0.9 (even some values over 0.95 in isolated spots), along with Shift of Tails values around 1. This suggests high confidence in anomalously warm high temperatures, although not extreme values based on the lower Shift of Tails. In terms of heat headlines, we will need to watch this closely, given the LREF ensemble exceedance probabilities of heat indices of 100 degree or warmer is around 30 to 50% for areas along and south of Highway 92 for Wednesday and Thursday. The probabilities of heat indices of 95 degree or warmer goes up drastically, to around 60 to 90% over most of our forecast area. Additionally, overnight lows might not dip below 75 degrees Monday night through Wednesday night, so this would continue stress from the heat - even at night. There is potential for some record warm low temperatures during this period. See the Climate section below for the current records. We will hold off on headlines for now, but Heat Advisories may be needed next week.

With all of this said, it bears repeating that any showers or storms that develop will help to limit temperatures, and therefore, heat indices. Ultimately, this appears most likely for areas along and north of Highway 30, where both NBM and LREF ensemble probabilities of measurable rainfall are 40 to 60%. In terms of strong to severe storms, there are some signals in the various machine-learning severe probs for at least a limited potential on Wednesday and Thursday as the mid-level ridge becomes more zonal for a time and a weak cold front sweeps through the area during that time with appreciable instability. Something for us to keep an eye on, but with it being further out, confidence isn't particularly high on severe weather at this time.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/

Issued at 1232 PM CDT Sat Aug 29 2026

Largely VFR conditions were seen across the area, under high- level clouds and an area of showers around CID northeast towards DBQ. The showers have been slowly dissipating over the last hour or so, and thus, visibilities haven't gone down as much as expected. At worst, high-end MVFR visibility reductions are possible under the showers. Otherwise, as the showers dissipate, southerly winds should strengthen this afternoon, gusting to around 25 knots. As the surface gusts diminish this evening, a period of low-level wind shear is expected area-wide as a 35 to 45 knot south-southwesterly low-level jet develops. Some showers and isolated thunderstorms are possible once again around or after sunrise, but confidence is pretty low on the exact coverage of this activity, so used PROB30 groups to highlight the more likely timing.

CLIMATE

Issued at 139 PM CDT Fri Aug 28 2026

Record Warm Low Temperatures:

August 31: KDBQ: 74/2000 KMLI: 75/2000

September 1: KDBQ: 73/1937 KMLI: 75/1913

September 2: KDBQ: 74/2011 KMLI: 77/1913

DVN WATCHES/WARNINGS/ADVISORIES

IA...None. IL...None. MO...None.